and(A,B) :- A, B.
or(A,_) :- A.
or(_,B) :- B.
equ(A,B) :- or(and(A,B), and(not(A),not(B))).
xor(A,B) :- not(equ(A,B)).
nor(A,B) :- not(or(A,B)).

:- op(900, fy,not).
:- op(910, yfx, and).
:- op(910, yfx, nand).
:- op(920, yfx, or).
:- op(920, yfx, nor).

% No funca
:- op( 1200, xfy, 'si' ).
X si Y :- Y, call(X).

yes :- true.
no :- fail.
false :- fail.